JP6470501B2 - Load drive circuit - Google Patents

Description

  The present invention relates to a load driving device.

  In a power supply box (hereinafter referred to as a unit) that distributes power in a vehicle, the use of semiconductors is expanding in order to meet demands for weight reduction and power saving. In order to further reduce the size, the use of IPD (Intelligent Power Device), which is a device in which a configuration of a conventional predriver + MOSFET (such as a device) or a driver and a control circuit having a protection function is integrated, is expanding. An example of the IPD is disclosed in Patent Document 1. Many of these devices have a built-in low-voltage cutoff function to prevent overheating due to an increase in on-resistance when the voltage drops.

JP 2011-55333 A

  Here, since the starter flows a large current, the terminal voltage of the battery decreases due to the internal resistance of the battery. As described above, in the vehicle, a phenomenon occurs in which the voltage temporarily decreases when the engine is started (particularly during cranking). There are loads that need to be operated even during cranking when the voltage temporarily drops in the vehicle, and in order to operate these, it is necessary to avoid the low voltage cutoff function. In order to avoid the low voltage cut-off function, for example, it is conceivable to install a spare battery for assisting power supply when starting the engine, or to provide a power supply system that is not involved in starting the engine. However, in these cases, the entire power system must be changed.

  Although it is conceivable to mount a DC / DC converter for voltage stabilization, there is a problem that a large component is required because of a large supply current.

  Note that the temporary voltage drop occurs not only at the time of cranking but also at the time of idle stop, for example, and the above problem is not limited to the time of cranking but is also a problem common to voltage drops occurring at other timings.

  The present invention solves such a problem, and the object of the present invention is not to change the entire power supply system, but to reduce the number of large parts and to reduce the voltage when the voltage drops. An object of the present invention is to provide a load driving device capable of driving a load while avoiding a blocking function.

  A load drive circuit according to the present invention includes a semiconductor relay that is turned off when a voltage from a battery is lowered and a predetermined operating voltage cannot be secured, and the load drive that cuts off power supply to the load when the semiconductor relay is turned off A low voltage detection circuit for detecting that the voltage from the battery is equal to or lower than a predetermined value; a negative voltage generation circuit for generating a negative voltage; and the voltage from the battery is predetermined by the low voltage detection circuit. Switch means for turning on and connecting the negative voltage generation circuit and the ground terminal of the semiconductor relay when it is detected that the value is less than or equal to the value;

  According to the load driving circuit of the present invention, when the voltage from the battery is detected to be equal to or lower than the predetermined value, the load driving circuit is turned on to connect the negative voltage generating circuit and the ground terminal of the semiconductor relay. The ground terminal becomes a negative voltage generated by the negative voltage generation circuit, and even if the voltage from the battery drops, the ground terminal is a negative voltage. Can be avoided. In addition, since the low-voltage cutoff function is avoided as described above, it is not necessary to provide a power supply system that is not involved in a spare battery or engine start, and it is not necessary to mount a DC / DC converter. Therefore, it is not necessary to change the entire power supply system, and the load can be driven while avoiding the low-voltage cutoff function when the voltage drops, while suppressing the required number of large parts.

  Further, in the load driving circuit according to the present invention, the negative voltage generation circuit is predetermined to be driven even when the voltage from the battery decreases and a predetermined operating voltage of the semiconductor relay cannot be secured. It is preferable that the negative voltage is generated when a signal indicating that driving is required for a low-voltage driving load that is a load is input, and generation of the negative voltage is prohibited when the signal is not input.

  This load drive circuit generates a negative voltage when a signal indicating that a low voltage drive load needs to be driven is input, and prohibits the generation of a negative voltage when a signal is not input. When driving is not required, power consumption can be suppressed without generating a negative voltage in the first place.

  In the load driving circuit according to the present invention, the load driving circuit further includes a control unit that outputs a ground switching on signal in a time zone in which the voltage from the battery is predicted to be a predetermined value or less. It is preferable that the negative voltage generating circuit is connected to the ground terminal of the semiconductor relay when the ground switching ON signal is output.

  According to this load drive circuit, since the ground switching on signal is output in the time zone in which the voltage from the battery is expected to decrease and the switch means connects the negative voltage generation circuit and the ground terminal of the semiconductor relay, Even if the switch means is not turned on by the output from the low voltage detection circuit when the voltage from the battery is below a predetermined value due to a failure in the voltage detection circuit etc., the voltage from the battery is expected to be below the predetermined value. In this time zone, the ground terminal voltage becomes a negative voltage, the operating voltage of the semiconductor relay can be secured, and the low voltage cutoff function can be avoided.

  In the load driving circuit according to the present invention, a control unit that outputs an on / off signal to the semiconductor relay, an in terminal of the semiconductor relay to which a signal corresponding to the on / off signal is input, and the ground terminal are provided. The semiconductor relay is configured such that a negative voltage from the negative voltage generation circuit is input to the ground terminal of the semiconductor relay when an off signal is output from the control unit to the semiconductor relay. It is preferable to further include a voltage conversion circuit that prevents the device from turning on.

  According to this load drive circuit, when an off signal is output to the semiconductor relay, the voltage conversion circuit that prevents the semiconductor relay from turning on by inputting a negative voltage to the ground terminal of the semiconductor relay. Prepare. For this reason, for example, when the in terminal of the semiconductor relay is 0 V and the ground terminal is a negative voltage, it is possible to prevent the semiconductor relay from being turned on by mistake.

  According to the load driving circuit of the present invention, it is possible to drive the load by avoiding the low voltage cutoff function at the time of a voltage drop while suppressing the necessary number of large parts without changing the whole power supply system. It is possible to provide a load driving device that can be used.

It is a circuit diagram showing an outline of a load drive circuit concerning an embodiment of the present invention. It is a circuit diagram which shows the detail of the voltage conversion circuit of the load drive circuit which concerns on this embodiment. It is a detailed circuit diagram which shows the principal part of the load drive circuit which concerns on this embodiment. 4 is a timing chart showing the operation of the load drive circuit according to the present embodiment. It is a circuit diagram which shows the modification of the load drive circuit which concerns on this embodiment.

  Hereinafter, the present invention will be described according to a preferred embodiment, but the present invention is not limited to the embodiment shown below, and can be appropriately changed without departing from the gist of the present invention.

  FIG. 1 is a circuit diagram showing an outline of a load driving circuit according to an embodiment of the present invention. A load drive circuit 1 shown in FIG. 1 is mounted on a vehicle and is configured as a unit provided between a battery B and a load L. The power supply 10, the control unit 20, and a plurality of IPDs (semiconductor relays) 30. And.

  The power supply 10 inputs a voltage from the battery B and generates a specified voltage (for example, 5V). For example, a power supply IC or the like is used. The control unit 20 outputs an on / off signal to each of the plurality of IPDs 30, and is configured by, for example, a microcomputer. The control unit 20 is supplied with a voltage from the power supply 10 and a signal to that effect when an ignition switch (a starter switch or a headlamp switch) is turned on.

  The plurality of IPDs 30 are semiconductor relays interposed between the battery B and the plurality of loads L, and cut off power supply to the loads when turned off. In FIG. 1, the connection lines from the battery B to the load L are not shown.

  The plurality of IPDs 30 have a low voltage cutoff function that turns off when the voltage from the battery B temporarily decreases and a predetermined operating voltage cannot be secured. This low-voltage cutoff function is a function for preventing overheating due to an increase in on-resistance when the voltage drops. Among such a plurality of IPDs 30, any one or more IPDs 31 are connected to a load L <b> 1 (hereinafter referred to as a low voltage driving load L <b> 1) that needs to be driven when the voltage from the battery B decreases.

Each of the plurality of IPDs 30 has a GND terminal (ground terminal) T _GND connected to the ground. Note that the IPD 31 connected to the low voltage drive load L1 is grounded via a diode D.

  In such a configuration, for example, when an ignition switch is turned on, a signal to that effect is input to the control unit 20 and operation is started. And an ON signal is output with respect to IPD30 connected to the some load L used as a drive object. As a result, the plurality of loads L are driven by being supplied with electric power.

  However, at the time of cranking in which the voltage from the battery B temporarily decreases when the engine is started, the IPD 30 is turned off due to the low voltage cutoff function. For this reason, when the voltage from the battery B decreases, the low voltage drive load L1 that needs to be driven is not driven.

  Therefore, the load driving circuit 1 according to the present embodiment includes a low voltage detection circuit 40, a negative voltage generation circuit 50, an OR circuit 61, an AND circuit 62, a ground line changeover switch (switch means) 70, a voltage conversion circuit 80, And a connection line l1.

  The low voltage detection circuit 40 is a circuit that detects that the voltage from the battery B is equal to or lower than a low voltage detection threshold (predetermined value). When the voltage is lower than the low voltage detection threshold, a low voltage detection signal S1 is output. To do. The low voltage detection signal S1 is input to the OR circuit 61.

  The OR circuit 61 receives a ground voltage changeover switch (hereinafter simply referred to as a switch) when either the low voltage detection signal S1 or the GND switch ON signal (ground switch ON signal) S2 from the control unit 20 is input. ) 70 is turned on. Here, the GND switching ON signal S2 is a signal that is output in a time zone in which the voltage from the battery B is predicted to be equal to or lower than the low voltage detection threshold in advance, such as during cranking. The GND switching ON signal S2 is continuously output in the time period.

  The AND circuit 62 outputs a negative voltage generation signal S5 when both the signal S3 output when the ignition switch is turned on and the signal S4 from the control unit 20 are input. Here, the signal S4 is a signal output when the control unit 20 is activated.

The negative voltage generation circuit 50 is a circuit that generates a negative voltage (for example, −2 V) lower than the ground side voltage (that is, 0 V) of the IPD 30. The output of the negative voltage generation circuit 50 is connected via the switch 70 to the GND terminal T _{GND of the} IPD 31 connected to the low voltage drive load L1.

  It is desirable that the GND switching ON signal S2 and the signal S4 are not output at a timing when the driving of the low voltage driving load L1 is not necessary. This is because it is not necessary to avoid the low voltage cutoff function at the timing when the low voltage drive load L1 is not driven. The timing at which the driving of the low voltage drive load L1 is not necessary can be determined by whether or not the activation request signal for the low voltage drive load L1 output from the host device is input to the control unit 20, for example. Therefore, the negative voltage generation circuit 50 generates a negative voltage when a start request signal (signal that requires driving) is input to the low voltage drive load L1, and generates a negative voltage when the start request signal is not input. Will be prohibited.

  FIG. 2 is a circuit diagram showing details of the voltage conversion circuit 80 of the load driving circuit 1 according to the present embodiment. For convenience of explanation in FIG. 2, the control unit 20, the IPD 31, the negative voltage generation circuit 50, the connection line l1, and the like are also illustrated.

As shown in FIG. 2, the voltage conversion circuit 80 includes resistors R1 and R3 and an N-type switching element S. The switching element S is, for example, a PNP transistor, the base is connected to the control unit 20 via the resistor R1, the emitter is connected to the power supply 10, and the collector is connected to the IN terminal (in terminal) T of the IPD 31 via the resistor R2. Connected to _IN . The base and emitter of the PNP transistor that is the switching element S are connected via a resistor R3.

The connection line l1 is intended to be connected to the IN terminal _{T IN} and GND terminals _{T GND} of Ipd31, it is on the connection line l1 resistor R4 is provided.

Next, the operation of the load driving circuit 1 according to this embodiment will be described. FIG. 3 is a detailed circuit diagram showing a main part of the load driving circuit 1 according to the present embodiment. As shown in FIG. 3, a limiting resistor R <b> 5 is provided between the OR circuit 61 and the N-channel FET that is the switch 70. Further, the path l3 branches from a portion between the OR circuit 61 and the limiting resistor R5 in the path l2 from the OR circuit 61 to the switch 70, and is connected to the negative voltage generation circuit 50. The source of the N-channel FET is connected to the negative voltage generation circuit 50, and the drain is connected to the GND terminal T _GND .

In such a circuit configuration, when the low voltage detection signal S1 and the GND switching ON signal S2 are not input to the OR circuit 61, the switch 70 is turned off. As a result, the GND terminal T _GND of the IPD 31 is connected to the ground via the diode D (refer to the [normal] GND current path of the broken line arrow). On the other hand, when the low voltage detection signal S1 or the GND switching ON signal S2 is input to the OR circuit 61, the switch 70 is turned on. As a result, the GND terminal T _GND of the IPD 31 is connected to the negative voltage generation circuit 50 and becomes a negative voltage (refer to the GND current path [when voltage drops] indicated by a solid line arrow).

  FIG. 4 is a timing chart showing the operation of the load driving circuit 1 according to the present embodiment. Note that the timing chart shown in FIG. 4 shows an operation that does not consider the GND switching ON signal S2.

As shown in FIG. 4, it is assumed that the voltage from battery B is V1 at time zero. The voltage at the GND terminal T _GND is 0V. Then, it is assumed that the voltage from the battery B starts to decrease from V1 at time t1, and reaches the low voltage detection threshold at time t2. As a result, the switch 70 is turned on, and the voltage at the GND terminal T _GND becomes a negative voltage generated by the negative voltage generation circuit 50. Next, at time t3, the voltage from the battery B becomes V2.

Here, the voltage value that is the voltage V2−negative voltage (see the range indicated by the arrow in FIG. 4 ) is equal to or higher than the operating voltage of the IPD 31. For this reason, the IPD 31 secures an operating voltage and does not function as a low-voltage cutoff function.

Thereafter, the voltage from battery B maintains V2, and the voltage from battery B begins to rise at time t4. When the low voltage detection threshold is exceeded at time t5, the switch 70 is turned off and the voltage at the GND terminal T _GND returns to 0V. The voltage from battery B reaches V3 at time t6, and thereafter V3 is maintained.

Next, the operation of the voltage conversion circuit 80 will be described with reference to FIG. First, in this embodiment, when the control unit 20 wants to turn on the IPD 31, the control unit 20 outputs an ON signal that becomes L level. Therefore, the switching element S is turned on, the voltage of the power source 10 is input to the IN terminal _{T IN.} On the other hand, since the GND terminal T _GND is grounded, it becomes 0 V and the IPD 31 is turned on.

On the other hand, when it is desired to turn off the IPD 31, an off signal that is at the H level is output. Thereby, the switching element S is turned off. In this case, the switch 70 is turned off, it becomes possible to IN terminal _{T IN} is also connected to ground via a connection line l1 not GND terminal _{T GND} alone, Ipd31 becomes possible to turn off. Furthermore, even if the switch 70 has been turned on, a negative voltage from the negative voltage generating circuit 50 is not GND terminal _{T GND} only, is also input to the IN terminal _{T IN} through the connection line l1. Therefore, the IPD 31 is turned off.

  FIG. 5 is a circuit diagram showing a modification of the load driving circuit 1 according to the present embodiment. For example, the connection line l1 is removed from the load drive circuit 1 shown in FIG. 2, and the control unit 20 outputs an ON signal that is H level when the IPD 31 is to be turned ON, and is OFF that is L level when it is desired to be OFF. A signal shall be output.

In this case, if you want to turn on the Ipd31, switching element S 'is a NPN transistor is turned on by the ON signal at the H level, the voltage from the power supply 10 is input to the IN terminal _{T IN.} On the other hand, since the GND terminal T _GND is grounded, it becomes 0 V and the IPD 31 is turned on.

When it is desired to turn off the IPD 31, the switch element S ′ is turned off by an L level off signal. Therefore, the IN terminal T _IN becomes 0V. Here, when the switch 70 is turned off, the GND terminal T _GND is connected to the ground, so that it becomes 0 V, and the IPD 31 is turned off. However, when the switch 70 is turned on, the IN terminal T _IN becomes 0V, and the GND terminal T _GND becomes a negative voltage, so the IPD 31 may be turned on. That is, the IPD 31 may turn on unintentionally.

Therefore, when the voltage conversion circuit 80 shown in FIG. 2 outputs an off signal from the control unit 20 to the IPD 31 in cooperation with the connection line 11, the negative voltage from the negative voltage generation circuit 50 becomes the GND terminal T. By inputting to the _GND , the IPD 31 is prevented from being turned on.

  Note that the case where the IPD 31 is turned off is a timing at which the low voltage drive load L1 connected to the IPD 31 does not need to be driven, so it seems that the negative voltage generation circuit 50 does not generate a negative voltage. . However, when the load drive circuit 1 according to the present embodiment performs drive control for a plurality of low voltage drive loads L1, it is necessary to drive any one of the plurality of low voltage drive loads L1. Sometimes, the negative voltage generation circuit 50 generates a negative voltage. That is, the IPD 31 may be turned on in any one of the plurality of low voltage drive loads L1, and the other low voltage drive loads L1 may be turned off. In such a case, the problem as shown in FIG. 5 may occur, so that the circuit configuration shown in FIG. 2 is useful.

As described above, according to the load driving circuit 1 according to the present embodiment, when the voltage from the battery B is detected to be equal to or lower than the low voltage detection threshold, the negative voltage generation circuit 50 and the GND of the IPD 31 are turned on. Since the terminal T _GND is connected, the GND terminal T _{GND of the} IPD 31 becomes a negative voltage generated by the negative voltage generation circuit 50. Even when the voltage from the battery B is lowered, the GND terminal T _GND is a negative voltage. Therefore, the operating voltage of the IPD 31 can be secured and the low voltage cutoff function can be avoided. In addition, since the low-voltage cutoff function is avoided as described above, it is not necessary to provide a power supply system that is not involved in a spare battery or engine start, and it is not necessary to mount a DC / DC converter. Therefore, it is not necessary to change the entire power supply system, and the load can be driven while avoiding the low-voltage cutoff function when the voltage drops, while suppressing the required number of large parts.

  In addition, a negative voltage is generated when a start request signal is input for the low voltage drive load L1, and generation of a negative voltage is prohibited when no signal is input. Therefore, when the low voltage drive load L1 is not required to be driven. In the first place, it is possible to suppress power consumption without generating a negative voltage.

In addition, since the GND switching ON signal S2 is output in the time zone in which the voltage from the battery B is expected to decrease and the switch 70 connects the negative voltage generation circuit 50 and the GND terminal T _{GND of the} IPD 31, for example, low voltage detection Even if the switch 70 is not turned on by the output from the low voltage detection circuit 40 when the voltage from the battery B is below the low voltage detection threshold due to a failure of the circuit 40 or the like, the voltage from the battery B is detected as a low voltage. In a time zone that is predicted to be equal to or lower than the threshold value, the ground side voltage becomes a negative voltage, the operating voltage of the IPD 31 can be secured, and the low voltage cutoff function can be avoided.

In addition, a voltage conversion circuit 80 is provided to prevent the IPD 31 from being turned on when a negative voltage is input to the GND terminal T _{GND of the} IPD 31 when an off signal is output to the IPD 31. For this reason, for example, when the IN terminal T _{IN of the} IPD 31 is 0 V and the GND terminal T _GND is a negative voltage, it is possible to prevent the IPD 31 from being erroneously turned on.

  As described above, the present invention has been described based on the embodiment, but the present invention is not limited to the above embodiment, and may be modified without departing from the gist of the present invention. For example, various resistors, switching elements S, and the like can be appropriately changed without departing from the spirit of the present invention.

  Furthermore, in the present embodiment, the IPD 30 has been described as an example of a semiconductor relay. However, the semiconductor relay may be a device in which a pre-driver (having a low voltage cutoff function) and a MOSFET are combined, for example. It may be.

  When the low voltage detection circuit 40 fails or when a disconnection or the like occurs in the path from the battery B to the low voltage detection circuit 40, the signal S4 is output immediately before or simultaneously with the GND switching ON signal S2. Also good. When disconnection or the like occurs in the path from the battery B to the low voltage detection circuit 40 at the time of failure of the low voltage detection circuit 40, the output from the OR circuit 61 is substantially the GND switching ON signal S2 from the control unit 20. It will be controlled only by. Therefore, the signal S4 may be output immediately before or simultaneously with the GND switching ON signal S2 in correspondence with the GND switching ON signal S2. Needless to say, a circuit for diagnosing a failure of the low voltage detection circuit 40 or a circuit for detecting a disconnection in the path from the battery B to the low voltage detection circuit 40 is required for the failure or the disconnection.

1: Load drive circuit 10: Power supply 20: Control unit 40: Low voltage detection circuit 50: Negative voltage generation circuit 61: OR circuit 62: AND circuit 70: Switch 80: Voltage conversion circuit B: Battery D: Diode L: Load L1 : low voltage load R1-R6: resistance S: switching element _T GND: GND terminal _T IN: IN terminal l1: connection line

Claims (4)

A load driving circuit having a semiconductor relay that turns off when a predetermined operating voltage cannot be secured due to a drop in voltage from the battery, and that cuts off power supply to the load when the semiconductor relay is turned off;
A low voltage detection circuit for detecting that the voltage from the battery is a predetermined value or less;
A negative voltage generation circuit for generating a negative voltage;
Switch means for turning on and connecting the negative voltage generation circuit and the ground terminal of the semiconductor relay when the low voltage detection circuit detects that the voltage from the battery is below a predetermined value;
A load driving circuit comprising: The negative voltage generation circuit needs to drive a low-voltage driving load that is a predetermined load when driving is required even when a predetermined operating voltage of the semiconductor relay cannot be secured due to a decrease in voltage from the battery. The load drive circuit according to claim 1, wherein the negative voltage is generated when a signal to that effect is input, and the generation of the negative voltage is prohibited when the signal is not input. A control unit that outputs a ground switching on signal in a time zone in which the voltage from the battery is predicted to be a predetermined value or less;
The switch unit is turned on when a ground switching on signal is output from the control unit to connect the negative voltage generation circuit and the ground terminal of the semiconductor relay. Item 3. The load driving circuit according to Item 2. A control unit that outputs an on / off signal to the semiconductor relay;
An in-terminal of the semiconductor relay to which a signal corresponding to the on / off signal is input, and a connection line connecting the ground terminal;
When the control unit outputs an off signal to the semiconductor relay, the semiconductor relay is turned on by inputting a negative voltage from the negative voltage generation circuit to the ground terminal of the semiconductor relay. Voltage conversion circuit to prevent,
The load driving circuit according to claim 1, further comprising:

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